The present invention relates to a method for preparing hydrocarbon cracking catalyst compositions, in particular relates to a method for preparing catalyst compositions which exhibit high catalytic activity, gasoline selectivity and thermal and hydrothermal stability, and further can produce a high-octane gasoline.
Catalytic cracking of hydrocarbon originally aims at the production of gasoline. Therefore, catalysts used herein are required to possess high catalytic activity and gasoline selectivity, and are preferred to be capable of producing a high-octane gasoline. In addition, the thermal and hydrothermal stability endurable for repeated uses is also one of the requisites for cracking catalysts because it is customary in the commercially practiced catalytic cracking process to repeat the operation which comprises regenerating the deactivated catalysts which have been used in the reaction and thereafter employing the thus regenerated catalysts again in the reaction.
In the typical hydrocarbon catalytic cracking process, there has generally been used the catalyst which comprises a crystalline aluminosilicate zeolite dispersed in a porous matrix selected from silica, silica-alumina, silica-magnesia and the like. When this catalyst is classified from the viewpoint of the exchangeable cations of the crystalline aluminosilicate zeolite, this catalyst can be roughly classified into the one in which the crystalline aluminosilicate zeolite dispersed in the porous matrix takes the hydrogen form and the other in which the crystalline aluminosilicate zeolite dispersed in the matrix is ion-exchanged with rare earth metal. The former catalyst is generally inferior in catalytic activity and gasoline selectivity but is advantageous in that it can produce a high-octane gasoline, as compared with the latter catalyst, and the latter catalyst, in contrast with this, is superior in catalytic activity and gasoline selectivity but is disadvantageous in that it can not produce a high-octane gasoline. However, the latter catalyst possesses the thermal and hydrothermal stability exceeding that of the former catalyst, because the crystalline aluminosilicate zeolite has been ion-exchanged by the rare earth metal in the case of the latter catalyst.
It is to be noted that even the former catalyst using the crystalline aluminosilicate zeolite taking the hydrogen form can improve the thermal and hydrothermal stability of the catalyst by using the so-called ultra-stable crystalline aluminosilicate zeolite. In such a case, however, merits and demerits as stated above are caused depending upon whether the ultra-stable crystalline aluminosilicate zeolite takes the hydrogen form or the rare earth form, that is when the former is used, it is impossible to expect the catalytic activity, gasoline selectivity and thermal and hydrothermal stability to such an extent that can be expected when the latter is used, and when the latter is used in contrast with this, it is impossible to produce a high-octane gasoline to such an extent as the use of the former does.
In the case of the conventional catalytic cracking catalysts which comprise a crystalline aluminosilicate zeolite dispersed in a porous matrix, in short, limits are set to the improvement of catalytic activity, gasoline selectivity and thermal and hydrothermal stability so far as said aluminosilicate zeolite takes the hydrogen form, and limits are set to the improvement of the octane number of the product gasoline so far as the aluminosilicate takes the rare earth form.